CYSTEINES IN THE SHAKER K+ CHANNEL ARE NOT ESSENTIAL FOR CHANNEL ACTIVITY OR ZINC MODULATION

We investigated whether the cysteine residues in Shaker potassium (K+) channels are essential for activation and inactivation gating or for modulation of activation gating by external zinc (Zn2+). Mutants of th e Shaker K+ channel were prepared in which all seven cysteine residues were replaced (C-less). These changes were made in both wild-type Sha ker H4 channels and in a deletion mutant (Delta 6-46) lacking N-type ( ''fast'') inactivation. Replacement of all cysteines left most functio nal properties of the K+ currents unaltered. The most noticeable diffe rence between the C-less and wild-type currents was the faster C-type inactivation of the C-less channel which could be attributed largely t o the mutation of Cys(462). This is consistent with the effects of pre viously reported mutations of nearby residues in the S6 region. There were also small changes in the activation gating of C-less currents. M odulation by external Zn2+ of the voltage dependence and rate of activ ation gating is preserved in the C-less channels, indicating that none of the cysteines in the Shaker K+ channel plays an important role in Zn2+ modulation.